1. Field of the Invention
The present invention relates to a hub and, more particularly, to a ratchet hub for a bicycle.
2. Description of the Related Art
A conventional hub for a bicycle in accordance with the prior art shown in FIGS. 11 and 12 comprises a shaft 60, a hub body 50 rotatably mounted on the shaft 60, a ratchet wheel 51 secured in the hub body 50 to drive the hub body 50 to rotate relative to the shaft 60 and having an inside provided with a plurality of oneway ratchet teeth 511, a drive seat 40 rotatably mounted on the shaft 60 and having a first end provided with a support base 42 which is rotatable in the ratchet wheel 51 and has a periphery provided with a plurality of receiving slots 421, a plurality of pawl members 43 each pivotally mounted in a respective one of the receiving slots 421 of the support base 42 and each meshing with the oneway ratchet teeth 511 of the ratchet wheel 51 so that the ratchet wheel 51 is combined with and rotatable with the support base 42 of the drive seat 40, a plurality of elastic members 44 each biased between the support base 42 of the drive seat 40 and a respective one of the pawl members 43, at least one first bearing 62 and at least one bushing 63 mounted between the drive seat 40 and the shaft 60, and at least one second bearing 620 mounted between the hub body 50 and the shaft 60. The drive seat 40 has a second end provided with a sprocket 41.
In assembly, the hub body 50 is connected to a wheel (not shown) of the bicycle, the shaft 60 is connected to a frame (not shown) of the bicycle, the sprocket 41 of the drive seat 40 meshes with and is driven by a chain (not shown) which is driven by a chainwheel (not shown) which is driven by a pedal (not shown) that is pedalled by a rider.
In operation, when the pedal is pedalled by the rider to move forward, the chainwheel is driven by the pedal to drive the chain which drives the sprocket 41 of the drive seat 40 so as to rotate the drive seat 40 forward relative to the shaft 60, so that each of the pawl members 43 is rotatable forward with the support base 42 of the drive seat 40. At this time, each of the pawl members 43 meshes with the oneway ratchet teeth 511 of the ratchet wheel 51 so that the ratchet wheel 51 is driven by each of the pawl members 43 to drive the hub body 50 to rotate relative to the shaft 60 so as to move the wheel forward. On the contrary, when the pedal is pedalled by the rider to move backward, the chainwheel is driven by the pedal to drive the chain which drives the sprocket 41 of the drive seat 40 so as to rotate the drive seat 40 backward relative to the shaft 60, so that each of the pawl members 43 is rotatable backward with the support base 42 of the drive seat 40. At this time, each of the pawl members 43 passes by the oneway ratchet teeth 511 of the ratchet wheel 51 so that the ratchet wheel 51 is released from the oneway ratchet teeth 511 of the ratchet wheel 51. Thus, the ratchet wheel 51 together with the hub body 50 is not driven by the drive seat 40, and the drive seat 40 idles in the backward direction.
However, when each of the pawl members 43 passes by the one-way ratchet teeth 511 of the ratchet wheel 51 during the backward rotation of the drive seat 40, each of the pawl members 43 touches the oneway ratchet teeth 511 of the ratchet wheel 51 to produce noise due to the friction, thereby easily causing an uncomfortable sensation to the rider. In addition, when the hub body 50 is rotated in the backward direction (e.g., when the wheel is rotated backward by the rider), the ratchet wheel 51 is also rotated in the backward direction. At this time, each of the pawl members 43 meshes with the one-way ratchet teeth 511 of the ratchet wheel 51 so that the ratchet wheel 51 drives each of the pawl members 43 to drive the drive seat 40 to rotate relative to the shaft 60 in the backward direction. Thus, the pedal is driven by the drive seat 40 to rotate backward so that the rider is easily hit and hurt by the pedal, thereby causing danger to the rider.